Wireless telecommunications systems are known. In those known systems, radio coverage is provided to user equipment, for example, mobile telephones, by geographical area. A base station is located in each geographical area to provide the required radio coverage. User equipment in the area served by a base station receives information and data from the base station and transmits information and data to the base station. In a high-speed packet access (HSPA) telecommunications network, data and information is sent between user equipment and a base station in data packets on a radio frequency carrier.
Information and data transmitted by the base station to the user equipment occurs on radio frequency carriers known as downlink carriers. Information and data transmitted by user equipment to the base station occurs on radio frequency carriers known as uplink carriers.
In known wireless HSPA telecommunication systems, user equipment can move between geographical base station coverage areas. Service provided to user equipment is overseen by a radio network controller (RNC). The radio network controller communicates with user equipment and base stations and determines which base station, and which cell of the geographical area served by that base station each user equipment is primarily connected to (known as the “serving cell”). Furthermore, a radio network controller acts to control and communicate with a base station and user equipment when user equipment moves from the geographical area served by one base station to a geographical area served by another base station.
A signal transmitted between user equipment and a base station over a radio channel typically experiences many propagation paths, for example, due to reflection, before arriving at a base station receiver. The signal carried on those paths each arrive at a different time, power and phase at the receiver. The sum of the different signal propagation paths at the receiver causes the total signal received to attenuate or amplify depending on the phases of the different received propagation paths.
Changes to the transmitter position or the transmitter surroundings causes the multiple propagation path signals to change, leading to fluctuation in the signal at the receiver. This characteristic is known as multipath fading or fast fading. Fast fading causes the signal to fluctuate over even a short time span. A signal may suffer significant attenuation due to fading or deep fade. A signal that has undergone deep fade may not be decodable.
Transmit diversity (TxDiv), is a method according to which a signal can be transmitted over two or more antennas. If a signal transmitted by a first antenna experiences a deep fade, the same signal transmitted on another antenna, typically experiences different radio conditions and propagation paths and may arrive with good quality.
Uplink transmit diversity at user equipment requires more than one antenna to be provided, and that a signal may be sent to a base station on one or more of those antenna(s). The signal arriving at a base station from two antennas may be combined by the base station and can thus result in a diversity gain at the base station of the transmitted signal. Further, if the signal transmitted using one antenna is particularly affected by fast fading, a signal transmitted using another antenna may be less affected by fast fading.
The requirements of a user having uplink transmission diversity may be contrary to other requirements in place within a network. Those requirements may conflict, leading to decreased efficiency of data transfer within a wireless telecommunication network as a whole.
Accordingly, it is desired to improve the robustness of a wireless telecommunications network having uplink transmit diversity functionality.